Lithium cobalt oxide cathode material, preparation method thereof and lithium ion battery

Abstract

The application provides a lithium cobaltate positive electrode material, a preparation method thereof and a lithium ion battery. The preparation method of the lithium cobaltate positive electrode material comprises the following steps: (1) mixing a large-particle-size cobalt precursor, a first small-particle-size cobalt precursor and a lithium source, and performing primary sintering to obtain large-particle-size primary sintered material; (2) mixing a second small-particle-size cobalt precursor and the lithium source, and performing primary sintering to obtain small-particle-size primary sintered material; and (3) mixing the large-particle-size primary sintered material in step (1) and the small-particle-size primary sintered material in step (2), and performing secondary sintering to obtain the lithium cobaltate positive electrode material. The preparation method provided by the application can significantly reduce the charge transfer impedance of the obtained lithium cobaltate positive electrode material, improve the lithium ion migration rate, and avoid the impedance increase problem caused by unreasonable grading; the influence of the material impedance on the battery performance is improved, and the battery performance is improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a lithium cobalt oxide cathode material, its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium cobalt oxide (LiCoO2), as the earliest commercially available cathode material for lithium-ion batteries, holds an irreplaceable position in the field of 3C digital products such as smartphones and laptops due to its advantages such as high volumetric energy density, high discharge voltage, and low self-discharge rate. It is also gradually being applied in small portable energy storage devices. The electrochemical performance of lithium cobalt oxide depends on the morphology, particle size distribution, and crystal structure of its precursors (mainly cobalt tetroxide, cobalt carbonate, and cobalt hydroxide). Among these, material impedance is a key indicator affecting its lithium-ion migration rate and charge transfer efficiency. Excessive impedance can lead to increased energy loss and decreased rate performance during battery charging and discharging, and in severe cases, it can also cause problems such as battery overheating and shortened cycle life.

[0003] Particle gradation technology, as an effective means of controlling the packing density and pore structure of powder materials, has been initially applied to the preparation of lithium cobalt oxide cathode materials. Its core logic is to fill the gaps between single-size particles by rationally combining lithium cobalt oxide cathode material particles of different sizes, thereby optimizing the material packing structure and improving the lithium-ion migration path and reducing impedance. However, currently, this technology cannot fully leverage the impedance-regulating effect of particle gradation, failing to meet the performance requirements of high-end batteries.

[0004] Therefore, how to solve the problem of impedance instability and poor battery performance in the current lithium cobalt oxide preparation process, especially the preparation of large particles, is an urgent issue that needs to be explored. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a lithium cobalt oxide cathode material, its preparation method, and a lithium-ion battery. The preparation method provided by the present invention, through two different stages of particle gradation, significantly reduces the charge transfer impedance of the resulting lithium cobalt oxide cathode material and increases the lithium-ion migration rate, while avoiding the impedance increase problem caused by unreasonable gradation; thus improving the impact of material impedance on battery performance and enhancing battery performance.

[0006] To achieve this objective, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a lithium cobalt oxide cathode material, the method comprising the following steps:

[0008] (1) Mix large-particle cobalt precursor, first small-particle cobalt precursor and lithium source, and sinter once to obtain large-particle sintered material;

[0009] (2) Mix the second small-particle cobalt precursor and lithium source, and sinter once to obtain small-particle sintered material;

[0010] (3) Mix the large particle sintering material described in step (1) and the small particle sintering material described in step (2), and perform secondary sintering to obtain the lithium cobalt oxide cathode material;

[0011] Wherein, the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the first small-particle-size cobalt precursor; the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the second small-particle-size cobalt precursor.

[0012] It should be noted that the large-particle-size cobalt precursor and the small-particle-size cobalt precursor in this invention are defined based on the median particle size Dv50 of the cobalt precursor. The larger the median particle size Dv50, the larger the particle size, and the smaller the median particle size Dv50.

[0013] As a preferred technical solution, the median particle size Dv50 of the large-particle-size cobalt precursor in step (1) is 10μm~17μm.

[0014] As a preferred technical solution, the median particle size Dv50 of the first small-particle-size cobalt precursor in step (1) and the second small-particle-size cobalt precursor in step (2) are each 2μm~4μm independently.

[0015] It should be noted that, in this invention, "each independently" refers to the selection between two features. Within the defined conditions, the conditions between the two features can be completely identical, completely different, or partially identical.

[0016] As a preferred technical solution, in step (1), the mass ratio of the large-particle-size cobalt precursor to the first small-particle-size cobalt precursor is (5~9):(5~1).

[0017] As a preferred technical solution, the raw materials used in the mixing in step (1) and the raw materials used in the mixing in step (2) each independently include a first additive.

[0018] As a preferred technical solution, step (1) of the large-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0019] As a preferred technical solution, step (1) the first small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0020] As a preferred technical solution, step (2) the second small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0021] As a preferred technical solution, the heating rate of the first sintering in step (1) is 2℃ / min~5℃ / min; the holding temperature after the first sintering in step (1) is 700℃~1100℃; and the holding time after the first sintering in step (1) is 8h~12h.

[0022] As a preferred technical solution, the heating rate of the first sintering in step (2) is 2℃ / min~5℃ / min; the holding temperature after the first sintering in step (2) is 700℃~1100℃; and the holding time after the first sintering in step (2) is 8h~12h.

[0023] As a preferred technical solution, the mixed raw materials in step (3) also include a second additive.

[0024] As a preferred technical solution, in step (3), the mass of the small particle sintering material is 15% to 30% of the mass of the large particle sintering material.

[0025] As a preferred technical solution, the sintering temperature of the secondary sintering in step (3) is 850℃~950℃; the sintering time of the secondary sintering in step (3) is 8h~10h.

[0026] As a preferred technical solution, in step (3), after the second sintering is completed, the second sintering material and the third additive are mixed and sintered a third time.

[0027] As a preferred technical solution, the sintering temperature of the three sintering processes is 700℃~900℃; the sintering time of the three sintering processes is 6h~7h.

[0028] In a second aspect, the present invention provides a lithium cobalt oxide cathode material, which is prepared by the preparation method described in the first aspect.

[0029] Thirdly, the present invention also provides a lithium-ion battery comprising the lithium cobalt oxide cathode material as described in the second aspect.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The preparation method provided by this invention first performs a gradation treatment in the initial lithium-ion sintering stage to obtain large-particle sintered material. This process initially fills the gaps between individual particles, optimizes the material's packing structure, and thus improves the lithium-ion migration path. Then, a second gradation treatment is performed with small-particle sintered material. After sintering, the particle packing density is further optimized, ensuring the integrity of the material's crystal structure. Even with doping, no new crystal defects are introduced. This significantly reduces the charge transfer impedance of the lithium cobalt oxide material, increases the lithium-ion migration rate, and avoids the impedance increase problem caused by unreasonable gradation. It improves the impact of material impedance on battery performance and enhances battery performance. Attached Figure Description

[0032] Figure 1 The image shows a large particle sintered material in step (1) of Embodiment 1 of the present invention.

[0033] Figure 2 This is an SEM image of the large particle sintered material in step (1) of Embodiment 4 of the present invention.

[0034] Figure 3 This is an SEM image of the large particle sintered material in step (1) of Embodiment 5 of the present invention.

[0035] Figure 4 This is an SEM image of the large particle sintered material in step (1) of Embodiment 6 of the present invention.

[0036] Figure 5 This is a SEM image of the large particle sintered material in step (1) of Comparative Example 2 of the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0038] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0041] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0042] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0044] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0045] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0046] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0047] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0048] In one embodiment, the present invention provides a method for preparing a lithium cobalt oxide cathode material, the method comprising the following steps:

[0049] (1) Mix large-particle cobalt precursor, first small-particle cobalt precursor and lithium source, and sinter once to obtain large-particle sintered material;

[0050] (2) Mix the second small-particle cobalt precursor and lithium source, and sinter once to obtain small-particle sintered material;

[0051] (3) Mix the large particle sintering material described in step (1) and the small particle sintering material described in step (2), and perform secondary sintering to obtain the lithium cobalt oxide cathode material;

[0052] Wherein, the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the first small-particle-size cobalt precursor; the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the second small-particle-size cobalt precursor.

[0053] Existing particle gradation schemes lack precise control over the gradation of large and small particles, and the gradation ratio is set in a single way, which cannot be flexibly adapted to product needs. This can easily lead to high battery impedance due to unreasonable particle stacking. At the same time, it can also lead to increased charge transfer resistance of lithium cobalt oxide material after sintering and slow lithium ion migration rate, which seriously restricts the overall performance of the battery.

[0054] To address this, the preparation method provided by this invention first performs a gradation treatment during the initial lithium-ion sintering stage to obtain large-particle sintered material. This process initially fills the gaps between individual particles, optimizes the material's packing structure, and thus improves the lithium-ion migration path. Then, a second gradation treatment is performed with small-particle sintered material. After sintering, the particle packing density is further optimized, ensuring the integrity of the material's crystal structure. Even with doping, no new crystal defects are introduced. This significantly reduces the charge transfer impedance of the lithium cobalt oxide material, increases the lithium-ion migration rate, and avoids the impedance increase problem caused by unreasonable gradation. It improves the impact of material impedance on battery performance and enhances battery performance.

[0055] In the preparation method of the present invention, the gradation treatment at different stages must work together to reduce porosity, improve the overall performance of the mixture, stabilize the crystal structure, and optimize lithium-ion transport.

[0056] In some embodiments, the median particle size Dv50 of the large-particle cobalt precursor in step (1) is 10 μm to 17 μm, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or 17 μm.

[0057] In some embodiments, the median particle size Dv50 of the first small-particle-size cobalt precursor in step (1) and the second small-particle-size cobalt precursor in step (2) are each independently 2μm to 4μm, for example 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm or 4μm, etc.

[0058] In some embodiments, in step (1), the mass ratio of the large-particle-size cobalt precursor to the first small-particle-size cobalt precursor is (5~9):(5~1), for example, 5:5, 6:4, 7:3, 8:2 or 9:1.

[0059] In step (1) of this invention, various mass ratios of the large-particle-size cobalt precursor and the first small-particle-size cobalt precursor can be tried to achieve the best balance between packing density and sintering activity. Further adjusting the mass ratio of the large-particle-size cobalt precursor to the first small-particle-size cobalt precursor to (5~9):(5~1) is beneficial to obtaining the optimal packing density, maximizing the filling of interparticle gaps, shortening the lithium-ion migration path, and reducing impedance.

[0060] In some embodiments, the raw materials used in the mixing in step (1) and the raw materials used in the mixing in step (2) also each independently include a first additive.

[0061] In the preparation process of step (1) and / or step (2) of this invention, a first additive is added as a dopant to dope lithium cobalt oxide. While giving full play to the role of the doping element, it can also avoid introducing impurity phases that would damage the integrity of the crystal structure, leading to a decrease in the stability of the material structure, which in turn affects the rate performance and cycle life of the battery, making it difficult to balance high structural integrity and excellent electrochemical performance. That is, the preparation method provided by this invention solves the problem of crystal structure damage caused by simultaneous doping treatment in the existing gradation process.

[0062] It is understood that the present invention does not limit the specific type of the first additive. Without departing from the overall technical concept of the present invention, those skilled in the art can use conventional dopant substances according to actual needs.

[0063] For example, but not in a limiting sense, the doping element in the first additive provided by the present invention includes, but is not limited to, at least one of Mg, Ti, Al, Ni, Mn, Cu, Cr, Zr, Ce, Y, Nb, Mo, Ga, Sn, Zn, V, W or La; the first additive includes oxides, hydroxides, halides, organic compounds, salts, etc. containing the above-mentioned doping elements, and the specific compound containing the doping element can also be adaptively selected and adjusted according to actual needs.

[0064] In some embodiments, the large-particle-size cobalt precursor in step (1) includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0065] In some embodiments, step (1) of the first small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0066] In some embodiments, step (2) of the second small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

[0067] It is understood that the types of cobalt precursors in steps (1) and (2) of this invention are not unique. Without violating the overall technical concept of this invention, cobalt-containing compounds of lithium cobalt oxide can be obtained by lithium-based lithium sintering. This invention applies to all of them.

[0068] For example, the cobalt-containing compounds in the cobalt precursor include, but are not limited to, one or more of cobalt tetroxide, cobalt oxide, cobalt hydroxide, cobalt chloride, cobalt sulfate, cobalt carbonate, cobalt oxalate, high cobalt oxide, high cobalt hydroxide, or cobalt hydroxyoxide.

[0069] Furthermore, the present invention coats the surface of the cobalt-containing compound matrix with metal oxides, which reduces surface defects in the cobalt precursor material and further reduces the interfacial impedance of the lithium cobalt oxide cathode material.

[0070] For example, but not limitingly, the metal oxide in the metal oxide coating layer of the cobalt precursor includes at least one of aluminum oxide (Al2O3), zirconium oxide (ZrO2), or magnesium oxide (MgO).

[0071] In some embodiments, the mass of the metal oxide coating layer in the cobalt precursor is 0.05wt% to 1.5wt% of the mass of the cobalt compound matrix, for example, 0.05wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, or 1.5wt%.

[0072] In some implementations, the cobalt precursors described in steps (1) and (2) may each independently include doping elements.

[0073] In some embodiments, the sintering heating rate in step (1) is 2℃ / min to 5℃ / min, for example, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min.

[0074] In some embodiments, the holding temperature after the first sintering heating in step (1) is 700℃~1100℃, such as 700℃, 725℃, 750℃, 775℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1025℃, 1050℃, 1075℃ or 1100℃, etc.

[0075] In some implementations, the holding time after the first sintering heating in step (1) is 8h~12h, for example 8h, 9h, 10h, 11h or 12h.

[0076] In some embodiments, the sintering heating rate in step (2) is 2℃ / min to 5℃ / min, for example, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min.

[0077] In some embodiments, the holding temperature after the first sintering heating in step (2) is 700℃~1100℃, such as 700℃, 725℃, 750℃, 775℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1025℃, 1050℃, 1075℃ or 1100℃, etc.

[0078] In some implementations, the holding time after the first sintering heating in step (2) is 8h~12h, for example 8h, 9h, 10h, 11h or 12h.

[0079] In the first sintering process of step (1) and step (2) of this invention, a relatively high sintering temperature is used for sintering treatment, especially when it is controlled to 1000℃~1100℃, which is more conducive to the formation of single crystal particles and improves structural stability.

[0080] In some embodiments, the raw materials mixed in step (3) also include a second additive.

[0081] In step (3) of this invention, a second additive can also be added as a coating agent. While the gradation sintering of large-particle-burning material and small-particle-burning material is carried out, the material is initially coated to suppress sintering side reactions, pre-regulate interface stability, and lay the structural foundation for subsequent modification and coating, thereby synergistically improving the cycle stability and thermal safety performance of lithium cobalt oxide.

[0082] Furthermore, the present invention does not limit the specific type of the second additive. Without departing from the overall technical concept of the present invention, those skilled in the art can make adaptive selections and adjustments based on actual needs.

[0083] For example, but not in a limiting sense, the coating element in the second additive includes at least one of Mg, Ti, Co, Al, Ni, Mn, Cu, Cr, Zr, Ce, Y, Nb, Mo, Ga, Sn, Zn, V, W, or La-based elements; the second additive includes oxides, hydroxides, halides, organic compounds, salts, etc. containing the above-mentioned coating elements, and the specific compound containing the coating element can also be adaptively selected and adjusted according to actual needs.

[0084] In some implementations, in step (3), the mass of the small particle sintering material is 15% to 30% of the mass of the large particle sintering material, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0085] In the present invention, after performing the gradation treatment in step (1), when performing the gradation treatment in step (3), the mass of the small particle sintering material is adjusted to 15% to 30% of the mass of the large particle sintering material, thereby optimizing the powder packing structure, improving the ion conduction efficiency of the material, and improving the electrical properties.

[0086] In some embodiments, the sintering temperature of the secondary sintering in step (3) is 850℃~950℃; the sintering time of the secondary sintering in step (3) is 8h~10h, for example 8h, 9h or 10h.

[0087] In some embodiments, in step (3), after the second sintering is completed, the second sintering material and the third additive are mixed and sintered a third time.

[0088] After the second sintering in step (3), the present invention adds a third additive for coating sintering treatment, forming a dense coating layer on the surface of the lithium cobalt oxide material. The coating layer isolates the electrolyte and suppresses side reactions.

[0089] Meanwhile, the present invention does not limit the specific type of the third additive. Without violating the overall technical concept of the present invention, those skilled in the art can make adaptive selections and adjustments according to actual needs.

[0090] For example, but not in a limiting sense, the coating element in the third additive includes at least one of Mg, Ti, Co, Al, Ni, Mn, Cu, Cr, Zr, Ce, Y, Nb, Mo, Ga, Sn, Zn, V, W, or La-based elements; the third additive includes oxides, hydroxides, halides, organic compounds, salts, etc. containing the above-mentioned coating elements, and the specific compound containing the coating element can also be adaptively selected and adjusted according to actual needs.

[0091] In some embodiments, the sintering temperature of the three sintering processes is 700℃~900℃, such as 700℃, 725℃, 750℃, 775℃, 800℃, 825℃, 850℃, 875℃ or 900℃.

[0092] In some embodiments, the sintering time for the three sintering processes is 6h to 7h, for example, 6h or 7h.

[0093] It should also be noted that the present invention does not specifically limit the lithium source in steps (1) and (2). The present invention is applicable to any conventional lithium-containing compound that can be sintered with lithium cobalt oxide; for example, the lithium source in step (1) and the lithium source in step (2) include, but are not limited to, at least one of lithium carbonate, lithium hydroxide, lithium oxalate, lithium nitrate or lithium acetate.

[0094] Optionally, in steps (1) and (2), the molar ratio of lithium in the lithium source to cobalt in the cobalt precursor is independently (1~1.1):1, for example, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.1:1, etc.

[0095] Optionally, the first sintering in step (1), the first sintering in step (2), the second sintering in step (3), and the third sintering are all carried out independently in an oxygen-containing atmosphere, which includes an air atmosphere and / or an oxygen atmosphere, etc.

[0096] In one embodiment, the present invention provides a lithium cobalt oxide cathode material, which is prepared by the preparation method described in the above embodiments.

[0097] In one embodiment, the present invention also provides a lithium-ion battery comprising the lithium cobalt oxide cathode material as described in the above embodiments.

[0098] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0099] Example 1

[0100] This embodiment provides a lithium cobalt oxide cathode material, the preparation method of which includes:

[0101] (1) Cobalt tetroxide, a large-particle cobalt precursor with a median particle size Dv50 of 16 μm, cobalt tetroxide, a first small-particle cobalt precursor with a median particle size Dv50 of 3.5 μm, lithium hydroxide, and magnesium oxide, a first additive, are mixed in a mixer in a solid phase. The mass ratio of the large-particle cobalt precursor to the small-particle cobalt precursor is 6:4, the molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.07:1, and the amount of the first additive added is 1.5 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0102] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1000℃ at a heating rate of 2℃ / min and holding for 10h. The sintered product was cooled to room temperature, crushed and sieved to obtain large particle sintered material (large particle lithium cobalt oxide sintered material).

[0103] (2) Cobalt tetroxide, a cobalt precursor with a median particle size Dv50 of 3.5 μm, lithium hydroxide, and alumina, a first additive, are mixed in a mixer in a solid phase. The molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.07:1, and the amount of the first additive added is 1.5 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0104] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1000℃ at a heating rate of 2℃ / min and holding for 10h. The sintered product was cooled to room temperature, crushed and sieved to obtain small particle sintered material (small particle lithium cobalt oxide sintered material).

[0105] (3) The large-particle sintering material, the small-particle sintering material and the second additive magnesium oxide are mixed in a solid phase. The mass of the second additive is 0.5wt% of the total mass of all sintering materials, and the mass of the small-particle sintering material is 20% of the mass of the large-particle sintering material. After mixing, the mixture is sintered in air at a sintering temperature of 900℃ for 8 hours. The product after the second sintering is cooled to room temperature to obtain the second sintered material.

[0106] (4) The secondary sintering material and zirconium oxide are mixed in a solid phase. The mass of zirconium oxide added is 0.05 wt% of the mass of the secondary sintering material. After mixing, the mixture is sintered three times at a sintering temperature of 800°C for 6 hours in an air atmosphere. After sintering, the mixture is cooled to room temperature, crushed and sieved to obtain the lithium cobalt oxide cathode material.

[0107] Example 2

[0108] This embodiment provides a lithium cobalt oxide cathode material, the preparation method of which includes:

[0109] (1) Cobalt tetroxide, a large-particle cobalt precursor with a median particle size Dv50 of 15 μm, cobalt tetroxide, a first small-particle cobalt precursor with a median particle size Dv50 of 2 μm, lithium hydroxide, and alumina, a first additive, are mixed in a mixer in a solid phase. The mass ratio of the large-particle cobalt precursor to the small-particle cobalt precursor is 6:4, the molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.05:1, and the amount of the first additive is 1.3 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0110] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1100℃ at a heating rate of 3℃ / min and holding for 8 hours. The sintered product was cooled to room temperature, crushed and sieved to obtain large particle sintered material (large particle lithium cobalt oxide sintered material).

[0111] (2) Cobalt tetroxide, a cobalt precursor with a median particle size Dv50 of 2 μm, lithium hydroxide, and alumina, a first additive, are mixed in a mixer in a solid phase. The molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.05:1, and the amount of the first additive is 1.3 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0112] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1100℃ at a heating rate of 3℃ / min and holding for 8 hours. The sintered product was cooled to room temperature, crushed and sieved to obtain small particle sintered material (small particle lithium cobalt oxide sintered material).

[0113] (3) The large-particle sintering material, the small-particle sintering material and the second additive magnesium oxide are mixed in a solid phase. The mass of the second additive is 0.6 wt% of the total mass of all sintering materials, and the mass of the small-particle sintering material is 20% of the mass of the large-particle sintering material. After mixing, the mixture is sintered in air at a sintering temperature of 850°C for 10 h. The product after the second sintering is cooled to room temperature to obtain the second sintered material.

[0114] (4) The secondary sintering material and zirconium oxide are mixed in a solid phase. The mass of zirconium oxide added is 0.1 wt% of the mass of the secondary sintering material. After mixing, the mixture is sintered three times at a sintering temperature of 900°C for 6 hours in an air atmosphere. After sintering, the mixture is cooled to room temperature, crushed and sieved to obtain the lithium cobalt oxide cathode material.

[0115] Example 3

[0116] This embodiment provides a lithium cobalt oxide cathode material, the preparation method of which includes:

[0117] (1) Cobalt tetroxide, a large-particle cobalt precursor with a median particle size Dv50 of 17 μm, cobalt tetroxide, a first small-particle cobalt precursor with a median particle size Dv50 of 4 μm, lithium hydroxide, and alumina, a first additive, are mixed in a mixer in a solid phase. The mass ratio of the large-particle cobalt precursor to the small-particle cobalt precursor is 6:4, the molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.03:1, and the amount of the first additive is 1.4 wt% of the total mass of all precursors, to obtain a homogeneous mixture.

[0118] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1050℃ at a heating rate of 4℃ / min and holding for 12h. The sintered product was cooled to room temperature, crushed and sieved to obtain large particle sintered material (large particle lithium cobalt oxide sintered material).

[0119] (2) The second smallest cobalt precursor with a median particle size Dv50 of 4 μm, cobalt tetroxide, lithium hydroxide, and the first additive alumina are mixed in a mixer in a solid phase, wherein the molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.03:1, and the amount of the first additive added is 1.4 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0120] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1050℃ at a heating rate of 4℃ / min and holding for 12h. The sintered product was cooled to room temperature, crushed and sieved to obtain small particle sintered material (small particle lithium cobalt oxide sintered material).

[0121] (3) The large-particle sintering material, the small-particle sintering material and the second additive magnesium oxide are mixed in a solid phase. The mass of the second additive is 0.7wt% of the total mass of all sintering materials, and the mass of the small-particle sintering material is 20% of the mass of the large-particle sintering material. After mixing, the mixture is sintered in air at a sintering temperature of 950℃ for 9 hours. The product after the second sintering is cooled to room temperature to obtain the second sintered material.

[0122] (4) The secondary sintering material and zirconium oxide are mixed in a solid phase. The mass of zirconium oxide added is 0.15 wt% of the mass of the secondary sintering material. After mixing, the mixture is sintered three times at a sintering temperature of 800°C for 7 hours in an air atmosphere. After sintering, the mixture is cooled to room temperature, crushed and sieved to obtain the lithium cobalt oxide cathode material.

[0123] Example 4

[0124] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of large-particle-size cobalt precursor to small-particle-size cobalt precursor is 5:5.

[0125] All other conditions remain the same as in Example 1.

[0126] Example 5

[0127] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of large-particle-size cobalt precursor to small-particle-size cobalt precursor is 7:3.

[0128] All other conditions remain the same as in Example 1.

[0129] Example 6

[0130] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of large-particle-size cobalt precursor to small-particle-size cobalt precursor is 8:2.

[0131] All other conditions remain the same as in Example 1.

[0132] Example 7

[0133] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the mass ratio of large-particle-size cobalt precursor to small-particle-size cobalt precursor is 4:6.

[0134] All other conditions remain the same as in Example 1.

[0135] Example 8

[0136] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the median particle size Dv50 of the large-particle-size cobalt precursor cobalt tetroxide is 10 μm, and the median particle size Dv50 of the first small-particle-size cobalt precursor cobalt tetroxide is 5 μm.

[0137] All other conditions remain the same as in Example 1.

[0138] Example 9

[0139] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, the median particle size Dv50 of the large-particle-size cobalt precursor cobalt tetroxide is 16 μm, and the median particle size Dv50 of the first small-particle-size cobalt precursor cobalt tetroxide is 1 μm.

[0140] All other conditions remain the same as in Example 1.

[0141] Example 10

[0142] The difference between this embodiment and embodiment 1 is that the holding temperature for the first sintering in step (1) of this embodiment is 800℃; the holding temperature for the first sintering in step (2) is 800℃.

[0143] All other conditions remain the same as in Example 1.

[0144] Example 11

[0145] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass of the small particle sintering material is 15% of the mass of the large particle sintering material.

[0146] All other conditions remain the same as in Example 1.

[0147] Example 12

[0148] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass of the small particle sintering material is 30% of the mass of the large particle sintering material.

[0149] All other conditions remain the same as in Example 1.

[0150] Example 13

[0151] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass of the small particle sintering material is 10% of the mass of the large particle sintering material.

[0152] All other conditions remain the same as in Example 1.

[0153] Example 14

[0154] The difference between this embodiment and embodiment 1 is that in step (2) of this embodiment, the mass of the small particle sintering material is 35% of the mass of the large particle sintering material.

[0155] All other conditions remain the same as in Example 1.

[0156] Comparative Example 1

[0157] The difference between this comparative example and Example 1 is that the preparation method provided in this comparative example does not involve a gradation process; that is, it uses cobalt tetroxide, a large-particle-size cobalt precursor, as the sole precursor. The specific preparation includes:

[0158] (1) Cobalt tetroxide, a large-particle-size cobalt precursor with a median particle size Dv50 of 16 μm, lithium hydroxide, and magnesium oxide, the first additive, are mixed in a mixer in a solid phase. The molar ratio of lithium in lithium hydroxide to cobalt in all precursors is 1.07:1, and the amount of the first additive is 1.5 wt% of the total mass of all precursors, to obtain a uniform mixture.

[0159] The mixture was sintered once in air atmosphere. The sintering conditions were: heating to 1000℃ at a heating rate of 2℃ / min and holding for 10h. The sintered product was cooled to room temperature, crushed and sieved to obtain large particle sintered material (large particle lithium cobalt oxide sintered material).

[0160] (2) The large-particle sintering material and the second additive magnesium oxide are mixed in a solid phase. The mass of the second additive is 0.5wt% of the total mass of all sintering materials. After mixing, the mixture is sintered in air at a sintering temperature of 900℃ for 8 hours. The product after the second sintering is cooled to room temperature to obtain the second sintered material.

[0161] (3) The secondary sintering material and zirconium oxide are mixed in a solid phase. The mass of zirconium oxide added is 0.05 wt% of the mass of the secondary sintering material. After mixing, the mixture is sintered three times at a sintering temperature of 800°C for 6 hours in an air atmosphere. After sintering, the mixture is cooled to room temperature, crushed and sieved to obtain the lithium cobalt oxide cathode material.

[0162] Figure 1 The SEM image of the large particle sintered material in step (1) of Embodiment 1 of the present invention is shown.

[0163] Figure 2 The SEM image of the large particle sintered material in step (1) of Embodiment 4 of the present invention is shown.

[0164] Figure 3 The SEM image of the large particle sintered material in step (1) of Embodiment 5 of the present invention is shown.

[0165] Figure 4 The SEM image of the large particle sintered material in step (1) of Embodiment 6 of the present invention is shown.

[0166] Figure 5 The SEM image of the large particle sintered material in step (1) provided in Comparative Example 2 of the present invention is shown.

[0167] from Figures 1 to 5As can be seen, in the lithium cobalt oxide cathode material provided by the present invention, small particles are precisely filled in the gaps between large particles, and the overall void gradually increases as the proportion of large particles increases.

[0168] Comparative Example 2

[0169] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, the first small-particle-size cobalt precursor cobalt tetroxide with a median particle size Dv50 of 3.5 μm is not added.

[0170] All other conditions remain the same as in Example 1.

[0171] Comparative Example 3

[0172] The difference between this comparative example and Example 1 is that this comparative example does not perform step (2), but directly performs step (3) on the large particle sintering material obtained in step (1), and does not add small particle sintering material in step (3).

[0173] All other conditions remain the same as in Example 1.

[0174] Powder compaction test

[0175] The materials obtained in the examples and comparative examples were subjected to powder compaction tests under the following conditions:

[0176] Take 0.2g of powder and compact it at 0MPa-200MPa to obtain the powder conductivity at 200MPa.

[0177] The test results are shown in Table 1.

[0178] Table 1

[0179]

[0180] Battery fabrication and performance testing

[0181] 1) Button batteries were prepared using the lithium cobalt oxide cathode materials provided in the examples and comparative examples as cathode active materials, respectively.

[0182] Positive electrode sheet: 80 wt% of positive electrode active material, 10 wt% of Super-P and 10 wt% of polyvinylidene fluoride (PVDF) are dispersed in N-methylpyrrolidone (NMP) solution to prepare electrode slurry, which is then coated on aluminum foil and dried and rolled to obtain positive electrode sheet.

[0183] Negative electrode: Lithium sheet is used as the negative electrode.

[0184] Membrane: Φ19 PP microporous membrane (Celgard2400).

[0185] Electrolyte: 1 mol / L LiPF6 mixed with EC, DMC and EMC (EC:DMC:EMC volume ratio = 1:1:1).

[0186] The above-mentioned positive electrode, separator, negative electrode and electrolyte are assembled to obtain a coin cell.

[0187] II. Performance Testing

[0188] The batteries prepared in the examples and comparative examples were subjected to performance tests under the following conditions:

[0189] (a) Cyclic capacity retention: At 45°C and a voltage range of 2.5~4.5V, the capacity retention was tested after 50 cycles of 1C charge and discharge.

[0190] (b) Rate performance: Discharge specific capacity at 0.5C / discharge specific capacity at 0.2C under a voltage range of 2.5~4.5V at 25℃; the rate performance at 0.5C / 0.2C is obtained by conducting charge and discharge tests.

[0191] (c) DC internal resistance (DCIR): Discharge the battery for 10 seconds and record the voltage (V1) and current (I1); then let it rest for 10 minutes and record the voltage (V2) and current (I2). Finally, calculate the internal resistance using the formula DCIR=(V1-V2) / (I2-I1).

[0192] The test results are shown in Table 2.

[0193] Table 2

[0194]

[0195] From Table 1 and Table 2, we can obtain:

[0196] The preparation method provided by this invention, through two different stages of particle gradation process, significantly reduces the charge transfer impedance of the obtained lithium cobalt oxide cathode material and increases the lithium ion migration rate, while avoiding the impedance increase problem caused by unreasonable gradation; it improves the influence of material impedance on battery performance and enhances battery performance.

[0197] Data analysis of Examples 1 and 4-7 shows that in step (1) of the present invention, the mass ratio of the large-particle-size cobalt precursor to the first small-particle-size cobalt precursor is controlled to be (5~9):(5~1), which better plays the role of pre-regulating interface stability in the subsequent gradation process of step (3), lays the structural foundation for subsequent modification and coating, and synergistically improves the cycle stability and thermal safety performance of lithium cobalt oxide.

[0198] Data analysis of Examples 1, 8, and 9 shows that the median particle size Dv50 of the large-particle-size cobalt precursor in step (1) of the present invention is 10 μm to 17 μm, and the median particle size Dv50 of the first small-particle-size cobalt precursor in step (1) and the second small-particle-size cobalt precursor in step (2) are each independently 2 μm to 4 μm, so as to avoid particle size imbalance, abnormal packing porosity, and decreased rate performance.

[0199] Data analysis of Examples 1 and 10 shows that when the types of large-particle-size cobalt precursors and small-particle-size cobalt precursors are the same, a relatively high primary sintering temperature, especially when controlled to 1000℃~1100℃, is more conducive to complete grain development, high crystallinity, and reduced lattice defects.

[0200] Data analysis of Examples 1 and 11-14 shows that, after the gradation treatment in step (1), when the gradation treatment in step (3) is carried out, the mass of the small particle sintering material is adjusted to 15% to 30% of the mass of the large particle sintering material, which further improves the overall pore structure and optimizes the ion conduction efficiency.

[0201] Data analysis of Example 1 and Comparative Examples 1-3 shows that in the preparation method of the present invention, the gradation treatment at different stages must work together to optimize the powder packing structure, improve the ion conduction efficiency of the material, and enhance the rate performance.

[0202] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a lithium cobalt oxide cathode material, characterized in that, The preparation method of the lithium cobalt oxide cathode material includes the following steps: (1) Mix large-particle cobalt precursor, first small-particle cobalt precursor and lithium source, and sinter once to obtain large-particle sintered material; In step (1), the mass ratio of the large-particle-size cobalt precursor to the first small-particle-size cobalt precursor is (5~9):(5~1). (2) Mix the second small-particle cobalt precursor and lithium source, and sinter once to obtain small-particle sintered material; (3) Mix the large particle sintering material described in step (1) and the small particle sintering material described in step (2), and perform secondary sintering to obtain the lithium cobalt oxide cathode material; Wherein, the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the first small-particle-size cobalt precursor; the median particle size Dv50 of the large-particle-size cobalt precursor is greater than the median particle size Dv50 of the second small-particle-size cobalt precursor.

2. The preparation method according to claim 1, characterized in that, The median particle size Dv50 of the large-particle-size cobalt precursor in step (1) is 10 μm to 17 μm; And / or, the median particle size Dv50 of the first small-particle-size cobalt precursor in step (1) and the second small-particle-size cobalt precursor in step (2) are each independently 2 μm to 4 μm; And / or, the raw materials used in the mixing of step (1) and the raw materials used in the mixing of step (2) also each independently include a first additive.

3. The preparation method according to claim 1 or 2, characterized in that, The large-particle-size cobalt precursor in step (1) includes a cobalt-containing compound matrix and a metal oxide coating layer on the surface of the cobalt-containing compound matrix; And / or, in step (1), the first small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

4. The preparation method according to claim 1 or 2, characterized in that, Step (2) The second small-particle-size cobalt precursor includes a cobalt-containing compound matrix and a metal oxide coating layer covering the surface of the cobalt-containing compound matrix.

5. The preparation method according to claim 1, characterized in that, The heating rate of the first sintering in step (1) is 2℃ / min~5℃ / min; the holding temperature after the first sintering in step (1) is 700℃~1100℃; and the holding time after the first sintering in step (1) is 8h~12h. And / or, the sintering heating rate in step (2) is 2℃ / min~5℃ / min; the holding temperature after the sintering heating in step (2) is 700℃~1100℃; and the holding time after the sintering heating in step (2) is 8h~12h.

6. The preparation method according to claim 1, characterized in that, The mixed raw materials in step (3) also include a second additive; And / or, in step (3), the mass of the small particle sintering material is 15% to 30% of the mass of the large particle sintering material; And / or, the sintering temperature of the secondary sintering in step (3) is 850℃~950℃; the sintering time of the secondary sintering in step (3) is 8h~10h.

7. The preparation method according to claim 1, characterized in that, In step (3), after the second sintering is completed, the second sintering material and the third additive are mixed and sintered a third time.

8. The preparation method according to claim 7, characterized in that, The sintering temperature for the three sintering processes is 700℃~900℃; the sintering time for the three sintering processes is 6h~7h.

9. A lithium cobalt oxide cathode material, characterized in that, The lithium cobalt oxide cathode material is prepared by the preparation method according to any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium cobalt oxide cathode material as described in claim 9.

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